1. Field of the Invention
The present invention relates to a relates to a hand held tool for cutting laminated glass and film-covered glass, such as automotive windshields and architectural windows, and an associated method for cutting laminated glass and film-covered glass.
2. Background Information
Laminated glass, which is a type of safety glass, utilizes two or more regular or specially strengthened glass sheets bonded together with a special plastic interlayer to form a clear, see-through barrier with enhanced impact and shatter resistance. Polyvinyl butyral (PVB) plastic is commonly used as the interlayer which enhances the glass further by increasing sound insulation and blocking nearly 99% of ultraviolet radiation. The interlayer maintains the layers of glass bonded even when broken, and the relative high strength of the interlayer prevents the glass from breaking up into large sharp pieces. This produces a characteristic “spider web” cracking pattern when the impact is not enough to completely pierce the laminated glass. Laminated glass is normally used when there is a possibility of human impact or where the glass could fall if shattered. Laminated glass is standard in automobile windshields and is routinely used in building architectural windows or curtain walls (a non-structural outer covering of a building), skylights, and in prisons. More recently, laminated glass is used for blast and hurricane protection for architectural windows.
Automobile windshields are a clear, see-through wind barrier which provides impact resistance from insects, road debris, vandalism, etc . . . , roof crush resistance, airbag support and resistance to occupant ejection. Windshields can become damaged during normal use and during vehicle crashes. When windshields fracture, the glass fragments are contained and occupant injury risk is minimized. It should be noted that the term windshield is used generally throughout North America while the term windscreen is the usual term in the British Isles and Australasia for all vehicles. Rear windows of automobiles are also constructed of glass laminates.
During automobile crashes, there are instances when the vehicle occupants become trapped within the vehicle, possibly in need of emergency assistance, but where the occupants cannot be accessed via the doors. When this occurs, emergency personnel are required to remove the windshield or rear window to access the occupants. There are two methods employed for windshield removal: 1) blunt impact or 2) cutting. Blunt impact with an object like a hammer or a fire axe can fracture or tear the windshield. Handheld or powered saws can cut windshield glass after creating an access hole. Each of these methods increases the risk of injury to the patients/vehicle occupants and/or the emergency personnel by flying glass debris and increased extrication time. The power saws additionally create a large amount of harmful silica dust, discussed further below, as it ribs apart a ribbon of the windshield that is slightly wider than the saw blade.
During normal use, windshields can become damaged by impacts from road debris or other materials and require replacement. After replacement, the vehicle inspection stickers must be replaced or transferred from the old windshield. Technicians routinely transfer the inspection stickers intact with a portion of the windshield by trimming the glass, protecting the sharp edges with tape and placing them on the vehicle dashboard. This process can be time consuming and increases the risk of personal injury.
Plastic films are commonly used to cover laminated and un-laminated glass to provide additional resistance to impact, fire, UV light, sound and blast.
Silica is a mineral compound made up of one silicon atom and two oxygen atoms (SiO2). Crystalline silica is formed when silica molecules are lined up in order and in crystal form. Crystalline silica is a component of glass and has been used in many other industries such as blast furnaces, cement manufacturing, glass and concrete mixing product manufacture, ceramics, clay, china pottery, electronic, foundry, sand-blasting and manufacturing abrasives, and many construction activities. Occupations having a high potential for exposure to crystalline silica dust (aka respirable quartz) are metal, coal, and nonmetal (except fuels) mining; foundry, stone clay, and glass production work; and agricultural, chemical production, highway repair, and tuck-pointing work. Thus silica dust is a known inhalation hazard. Workers may be at risk of silicosis from exposure to silica dust when high-velocity impact shatters the sand into smaller, respirable (<0.5 to 5.0 μm in diameter) dust particles. According to the American Thoracic Society silicosis is a disease where scar tissue forms in the lungs and reduces the ability to extract oxygen from the air. Symptoms of silicosis can be acute, accelerated, or chronic. According to the National Institute for Occupational Safety and Health acute silicosis may develop within weeks and up to 5 years after breathing large amounts of crystalline silica. Accelerated silicosis may develop shortly after exposure to high concentrations of respirable crystalline silica, whereas chronic silicosis occurs after 10 years of exposure to relatively low concentrations of crystalline silica. OSHA has estimated that more than 2 million workers are exposed to crystalline silica dust in the general, maritime, and construction industries, and that more than 100,000 workers have high-risk exposure to airborne silica dust through construction and mining operations. Further it has been estimated that there were an estimated 3,600-7,300 newly recognized silicosis cases per year in the United States from 1987 to 1996 and that between 1990 and 1996, 200-300 deaths per year were known to have occurred where silicosis was identified as a contributing cause on death certificates. Further, the International Agency for Research on Cancer classified crystalline silica as a known human carcinogen with exposure to crystalline silica associated with an increased risk of developing lung cancer. Previous studies also documented an association between airborne silica exposure and other health problems, including chronic obstructive pulmonary disease, rheumatoid arthritis, scleroderma, Sjogern's syndrome, lupus, and renal disease.
In fields other than glass, shearing tools have been designed such as disclosed in U.S. Pat. No. 7,637,016, which is incorporated herein by reference, which discloses hand-held cutting tools used to cut fiber-cement siding. U.S. Published Patent Application 2006-0213343, which is also incorporated herein by reference, discloses waste ejecting blade assemblies for hand-held cutting tools and methods for cutting fiber-cement materials. U.S. Published Patent Application 2004-0050223, which is also incorporated herein by reference, discloses blade assemblies for reciprocating wallboard tools and methods for cutting wallboard. See also U.S. Published Patent Application 2003-0029043, Design Pat. D443,806, U.S. Pat. Nos. 5,993,303, 5,992,024, 5,566,454, 4,173,069, 3,808,682, and 2,934,822 which are also incorporated herein by reference. These tools provide certain advantages for their particular designated work products but fail to provide effective or efficient, or even useful, laminated glass cutting tools as the blade sets of these tools tend to crush the glass layers without shearing the laminating layer resulting in a jammed tool when attempted to be implemented with laminated glass.
A refined method for cutting laminated glass and film-covered glass would minimize personal injury associated with vehicle occupant extrications, as well as laminated glass and film-covered glass repair and replacement. Further, the time needed for cutting will be greatly reduced. Further there is a need to perform such glass processing in a manner that minimizes airborne silica, particularly for Emergency workers, whom do not always take the time needed to don mask or other protective equipment when responding to a vehicle crash.